Resource: Remove unused `_use_builtin_script()` virtual method

And another piece of dead code found while searching for "use_builtin".

(cherry picked from commit 6e9439198c03ac6b5786eefe8dc3408cf1c4d3b6)

core/resource.h

@@ -59,8 +59,6 @@ class Resource : public Reference {
 	String path_cache;
 	int subindex;
 
-	virtual bool _use_builtin_script() const { return true; }
-
 #ifdef TOOLS_ENABLED
 	uint64_t last_modified_time;
 	uint64_t import_last_modified_time;

modules/visual_script/visual_script_editor.cpp

@@ -2328,10 +2328,6 @@ void VisualScriptEditor::drop_data_fw(const Point2 &p_point, const Variant &p_da
 				pset.instance();
 				pset->set_call_mode(VisualScriptPropertySet::CALL_MODE_INSTANCE);
 				pset->set_base_type(obj->get_class());
-				/*if (use_value) {
-						pset->set_use_builtin_value(true);
-						pset->set_builtin_value(d["value"]);
-					}*/
 				vnode = pset;
 			} else {
 				Ref<VisualScriptPropertyGet> pget;